The present invention relates to a continuously variable transmission (CVT) for traction drives which is used to transmit rotation from an input side to an output side while continuously varying the speed by traction drive in a power transmission device of an automobile, industrial machinery and so forth. More particularly, this invention relates to a traction drive rotary assembly including a rolling element having a traction contact surface that can exhibit excellent traction properties.
CVTs have been variously researched because of their excellent power transmission properties and absence of speed-change shock. In particular, researches have been conducted on systems (traction drive system: rolling contact system) that transmit power between traction contact surfaces by means of traction oil in order to transmit large power.
The traction drive system has a mechanism applicable to high-power engines. FIG. 1 shows a basic structure of traction drive CVTs. Traction drive CVT 1 includes two metal rolling elements, namely, two disks coaxially arranged, namely, input disk 3 circumferentially fixed on input shaft 2 and output disk 5 circumferentially fixed on output shaft 4, and power rollers 6 interposed between input and output disks 3 and 5. Input and output disks 3 and 5 are rotatable about axes, respectively. Input and output disks 3 and 5 have annular concave traction contact surfaces 3a and 5a, respectively. Traction contact surfaces 3a and 5a form a toroidal cavity in which each power roller 6 is disposed. Power roller 6 has annular convex traction contact surface 6a contacted with traction contact surfaces 3a and 5a of input and output disks 3 and 5 via traction oil. Power roller 6 is rotatable so as to transmit the torque from input disk 3 and output disk 5. Power roller 6 is also adapted to swing about a pivot perpendicular to the rotation axis and thus pivotally move on traction contact surfaces 3a and 5a of input and output disks 3 and 5. As power roller 6 swings, the contact between traction contact surface 6a of power roller 6 and traction contact surfaces 3a and 5a of input and output disks 3 and 5 is displaced. This causes change in a ratio of the torque radius of input disk 3 to that of output disk 5 to thereby continuously change the speed-change ratio. Such a traction drive CVT is disclosed in Japanese Patent Application First Publication No. 62-251559, which is incorporated by reference herein. Traction drive CVT 1 shown in FIG. 1 is a so-called half-toroidal CVT.
The rolling elements of the traction drive CVT, namely, input disk 3, output disk 5 and power roller 6 as shown in FIG. 1, are required to have excellent traction properties and high rolling fatigue life properties under high temperature and high bearing pressure. In addition, in consideration of the future burden on the environment, it is required that vehicle weight be reduced to achieve further improvement of fuel economy. In order to meet the requirement, a unit size of the traction drive CVT must be reduced. In the case of units of the same size, it is necessary to increase the power that can be transmitted.
In consideration of the problems of the related art described above, the object of the present invention is to provide a traction drive rotary assembly capable of transmitting large power and having excellent traction properties.
According to one aspect of the present invention, there is provided a traction drive rotary assembly for transmission power via traction oil, the traction drive rotary assembly comprising:
a plurality of rolling elements including traction contact surfaces associating with each other to transmit the power between the rolling elements, at least one of the traction contact surfaces having a surface microstructure including grooves and protrusions alternately arranged,
the surface microstructure being represented by an unfiltered primary profile curve that includes recesses and projections corresponding to the grooves and the protrusions, respectively, each projection including a portion located higher than a center line of the unfiltered primary profile curve, the portion having a shape selected from a generally trapezoidal shape with rounded corners, a generally crowning shape, a generally elliptic arc shape, a generally sinusoidal shape and a generally triangular shape with a rounded apex,
wherein a ratio xcex/AMP of a wavelength xcex of the unfiltered primary profile curve to a half depth AMP of each recess is in a range of 50-400.
According to a further aspect of the present invention, there is provided a continuously variable transmission for traction drives, comprising:
input and output disks arranged rotatably and coaxially, the input and output disks having annular concave traction contact surfaces; and
power rollers rotatably disposed between the input and output disks, the power rollers each having an annular convex traction contact surface contacted with the traction contact surfaces of the input and output disks, the power rollers being pivotally moveable on the traction contact surfaces of the input and output disks,
the traction contact surface of at least one of the input and output disks and the power rollers having a surface microstructure including grooves and protrusions alternately arranged,
the surface microstructure being represented by an unfiltered primary profile curve that includes recesses and projections corresponding to the grooves and the protrusions, respectively, each projection including a portion located higher than a center line of the unfiltered primary profile curve, the portion having a shape selected from a generally trapezoidal shape with rounded corners, a generally crowning shape, a generally elliptic arc shape, a generally sinusoidal shape and a generally triangular shape with a rounded apex,
wherein a ratio xcex/AMP of a wavelength xcex of the unfiltered primary profile curve to a half depth AMP of each recess is in a range of 50-400.